The present invention relates to a liquid crystal display device used for a personal computer, a work station and others, and in particular to a liquid crystal display device employing an attachment structure of a chip component capable of improving productivity and productive capacity of circuit boards of the liquid crystal display device.
Liquid crystal display modules of the STN (Super Twisted Nematic) type or the TFT (Thin Film Transistor) type are widely used as a display device of a notebook personal computer and the like.
Such liquid crystal display modules are comprised of a liquid crystal display panel having a driver circuit section disposed at its periphery and a backlight unit for illuminating the liquid crystal display panel.
The backlight unit includes in a molded case, a light guide for directing light emitted from a light source to uniformly illuminate the entire display area of the liquid crystal display panel, a cold-cathode fluorescent lamp serving a line light source disposed in the vicinity of the side of the light guide in parallel with the side of the light guide, a light diffusing sheet disposed on the light guide, a lens sheet (also called a prism sheet) disposed on the light diffusing sheet, and a reflector sheet extending below the light guide, for example.
Such techniques are described in Japanese Patent Publication No. Sho 60-19474 and Japanese Utility Model Application Laid-open No. Hei 4-22780, for example.
Generally, a liquid crystal display module is equipped with a driver circuit board (TCON board) having mounted thereon a display control device for controlling and driving the driver circuit section of the liquid crystal display panel, and chip components such as resistor elements are soldered on the driver circuit board.
A lead (Pb)-containing solder paste (Sn-37Pb) has been used for soldering the chip components. But there is a demand that lead-free solder pastes should be used instead of lead-containing solder pastes so as to improve mechanical characteristics (adhesion). However, there has been a problem in that, if a lead-free solder (e.g., an Sn-3.5 Ag-0.7Cu solder) is used instead of a conventional solder (Sn-37 Pb), defective soldering of chip components (a chip standing phenomenon) occurs frequently due to a higher melting point of the lead-free solder. While the melting point of the Sn-37Pb system solder is 183xc2x0 C., the melting points of lead-free solders are usually equal to or more than 200xc2x0 C. Greater detail of lead-free solders is contained in U.S. Pat. No. 5,942,185 issued on Aug. 24, 1999 and U.S. Pat. No. 5,918,795 issued on Jul. 6, 1999. These two patents are incorporated by reference herein for the purpose of disclosure.
Whether the above-mentioned lead-free solder is used or not, the above-described defective soldering occur according to manners of heating the boards during the soldering step. Frequency of occurrences of defective soldering is distinctly increased only by accelerating slightly the speed of increasing the temperature of heating the board or by increasing slightly the temperature of heating the board, for example, and therefore, especially if the lead-free solder is used in the assembling step of the driver circuit board, measures against defective soldering is more necessary.
Techniques for preventing defective soldering by modifying the shape of the land areas formed on the printed circuit boards are disclosed by Japanese Patent Application Laid-open No. Hei 2-23694 (laid-open on Jan. 25, 1990) and a complete specification of Japanese Utility Model Application Laid-open Hei 2-36074 laid-open on Mar. 8, 1990 which is recorded in a microfilm of the Japanese Patent Office, for example. However, neither of the techniques disclosed in the two references could not solve the problem of defective soldering completely.
The present invention is made to solve the problem with the prior art, and it is an object of the present invention to provide a liquid crystal display device capable of reducing defective soldering of chip components to its circuit board.
The above-mentioned and other objects and novel features of the present invention will become apparent by reference to the following description and the accompanying drawing.
The following is a representative one of liquid crystal display devices of the present invention disclosed in this application.
In accordance with an embodiment of the present invention, there is provided a liquid crystal display device comprising a liquid crystal display panel including a pair of opposing substrates and a liquid crystal layer sandwiched between the pair of opposing substrates, at least one driver circuit disposed at a periphery of one of the pair of opposing substrates for applying a drive voltage to the liquid crystal layer, a circuit board mounting thereon a display control circuit for controlling and driving the at least one driver circuit, the circuit board including a chip component having a pair of electrodes disposed at respective ends thereof, the pair of electrodes being soldered to a pair of land areas disposed on the circuit board, respectively, a portion of a respective one of the pair of land areas being covered with a protrusion of a solder resist layer protruding from a center of a side of the respective one of the pair of land areas opposite from mutually facing sides of the pair of land areas toward a center of the respective one of the pair of land areas, and a distance L between the protrusions of the solder resist layer satisfying the inequality Lxe2x89xa7EL, where EL is a distance between outer ends of the pair of electrodes of the chip component.
In accordance with another embodiment of the present invention, there is provided a liquid crystal display device comprising a liquid crystal display panel including a pair of opposing substrates and a liquid crystal layer sandwiched between the pair of opposing substrates, at least one driver circuit disposed at a periphery of one of the pair of opposing substrates for applying a drive voltage to the liquid crystal layer, a circuit board mounting thereon a display control circuit for controlling and driving the at least one driver circuit, the circuit board including a chip component having a pair of electrodes disposed at respective ends thereof, the pair of electrodes being soldered to a pair of land areas disposed on the circuit board, respectively, a portion of a respective one of the pair of land areas being covered with a protrusion of a solder resist layer protruding from a center of a side of the respective one of the pair of land areas opposite from mutually facing sides of the pair of land areas toward a center of the respective one of the pair of land areas, a distance L between the protrusions of the solder resist layer satisfying an inequality Lxe2x89xa7EL, where EL is a distance between outer ends of the pair of electrodes of the chip component, and a length h of the protrusion of the solder resist layer as measured in a protruding direction thereof satisfying an inequality hxe2x89xa7EL/10.
The present invention can reduce the excess amount of a solder adhering to sides of electrodes at both ends of a chip component contributory to the chip-standing phenomenon and consequently, can reduce defective soldering of the chip component (a chip-standing defect).